Feline chlamydiosis is a common conjunctival and respiratory disease of cats known as feline pneumonitis (FPn). This highly contagious disease is characterized by sneezing and coughing and is accompanied by mucopurulent ocular and nasal discharges. All age groups of cats are susceptible and, although mortality is not great, infected kittens and older cats may become severely debilitated. Because of its extreme infectivity, feline chlamydiosis constitutes a major problem in pet hospitals, clinics and catteries. There is some thought that persistent genital tract infection by Chlamydia psittaci is a cause of reproductive failure in catteries.
Vaccination studies with modified-live compositions of Chlamydia psittaci have produced conflicting results. Cello (Am. J. Vet. Med. Assoc. 158:932-938, 1971) indicated that such vaccines demonstrated no significant protection of cats. Shewen, et al. (Can. J. Comp. Vet. Res. 44:244-251, 1980) indicated partial protection while McKercher (Am. J. Vet. Res. 13:557-561, 1952) and others indicated almost complete protection by such vaccines. However, because the vaccinated cats are receiving live Chlamydia psittaci. some vaccine organisms can shed to other cats and reversion has been proposed to occur.
Studies with inactivated chlamydia vaccines have produced mixed results and unacceptable local and systemic reactions in vaccinated cats. Comparative challenge studies conducted with four inactivated vaccine preparations and a commercial modified-live vaccine demonstrated that the inactivated preparations conferred virtually no protection against chlamydia infection in cats (Shewen et al, Can. J. Comp. Med. 44:244-30 251, 1980). An inactivated Chlamydia psittaci vaccine has been described by Chu et al. (U.S. Pat. No. 5,242,686). However, this vaccine is not purified and causes unacceptable local reactions when administered to cats (COMPENDIUM).
With the knowledge that modified-live chlamydia vaccines can shed to other animals, can recombine with field strains of Chlamydia psittaci and can revert to virulence, and the knowledge that currently-marketed inactivated chlamydia vaccines are either ineffective or cause unacceptable local reactions, there is a need for effective, non-reactive chlamydia vaccines. It is an object of the present invention to provide an inactivated feline chlamydia vaccine composition having high immunogenicity without having a high antigenic mass. It is another object of this invention to provide a simple process for producing a suitable purified Chlamydia psittaci for production of a non-reactive, effective vaccine as a monovalent preparation or in a combination with other feline antigens.
The present invention discloses an inactivated, immunogenically effective Chlamydia psittaci which is incorporated into chlamydia vaccines in minute quantities (low antigen load or low antigen mass) and which is purified away from the cells in which it is grown so as to produce a vaccine which, when administered to cats is non-reactive but highly effective. In such vaccine the immunogenically effective, low antigen mass, purified Chlamydia psittaci is combined with effective amounts of an adjuvant and a pharmaceutically acceptable carrier or diluent therefor. The purification process for production of the Chlamydia psittaci incorporates several steps which include use of the yolk sac membrane, washed free of yolk material, as seed to inoculate a mammalian cell line such as the Buffalo Green Monkey (BGM) cell line available from Bio Whittaker and, after completion of the cell destruction by the chlamydia (cytopathic effect or CPE), removing the cells and cellular debris from the vaccine preparation prior to inactivation. One of the major requirements of this invention is that the cell line used for growth of the Chlamydia psittaci be destroyed by the organism within 7 days of infection with the Chlamydia psittaci (demonstrate at least 80% CPE within 7 days of infection with the chlamydia).